Innocent Murmurs
Innocent murmurs, also known as flow murmurs, are very common in children. They are caused by fast blood flow during systole.
Innocent murmurs have typical features, all beginning with S:
- Soft
- Short
- Systolic
- Symptomless
- Situation dependent (the murmur gets quieter with standing, or only appears when the child is unwell or feverish)
Innocent murmurs with no concerning features may not require further investigation. Features prompting referral:
- Murmur louder than 2/6
- Diastolic murmurs
- Louder on standing
- Other symptoms, such as failure to thrive, feeding difficulty, cyanosis or shortness of breath
Pan-Systolic Murmurs
Pan-systolic murmurs occur throughout the systolic contraction of the heart, between the first and second heart sounds (S1 and S2).
Causes of pan-systolic murmurs in children include:
- Mitral regurgitation, heard loudest in the mitral area (5th intercostal space, mid-clavicular line)
- Tricuspid regurgitation, heard loudest in the tricuspid area (5th intercostal space, left sternal border)
- Ventricular septal defect, heard loudest at the left lower sternal border
Ejection-Systolic Murmurs
Ejection-systolic murmurs occur during systole between S1 and S2. They have a crescendo-decrescendo character, building and then falling in intensity, with a peak in the middle. This matches the flow during systole, which is slowest at the start and end, and fastest in the middle.
Causes of pan-systolic murmurs in children include:
- Aortic stenosis, heard loudest in the aortic area (2nd intercostal space, right sternal border)
- Pulmonary stenosis, heard loudest in the pulmonary area (2nd intercostal space, left sternal border)
- Hypertrophic obstructive cardiomyopathy, heard loudest in the 4th intercostal space at the left sternal border
Splitting of the Second Heart Sound
The second heart sound (S2) is caused by the closure of the aortic and pulmonary valves at the end of systole. A “split” second heart sound occurs when the aortic and pulmonary valves close at different times. The causes include:
- Normal during inspiration
- Atrial septal defect (fixed split)
- Pulmonary valve stenosis (wide split)
During inspiration, the chest wall and diaphragm expand and create negative intrathoracic pressure, which pulls the lungs and heart open. Negative intrathoracic pressure causes increased filling of the right atrium and ventricle from the systemic venous circulation. It takes longer for the right ventricle to empty the greater volume of blood, causing a slight delay in the pulmonary valve closing compared with the aortic valve. Therefore, there is a “split” second heart sound during inspiration.
An atrial septal defect allows blood to flow from the left atrium to the right atrium, increasing the volume of blood the right ventricle has to empty before the pulmonary valve can close. The atrial septal defect causes a “fixed split” second heart sound, which does not vary during inspiration and expiration.
Pulmonary valve stenosis can cause a “widely split” second heart sound, as it takes notably longer for the right ventricle to empty through the narrow pulmonary valve compared with the left ventricle.
Investigations
Echocardiogram is the gold-standard for diagnosing structural heart disease.
Additional investigations to consider include:
- ECG to diagnose arrhythmia
- Chest x-ray to diagnose other pathology related to symptoms
Last updated November 2024
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